GTRacer4
How do you get different troops?
Build them in barracks=infantry, stable=cavalry, workshop=siege weapons. To be able to build more than basic troop types [phalanx, legionnaires, clubswingers] you need to build an academy, and few different buildings than are required to allow you to 'develop' new unit type.
Those required buildings are similar for all tribes, what exactly do you need for a particular unit, can be seen in that unit description, at the bottom. [to see the description, go to barracks, click on your basic unit's name and small window will pop up, just use arrows at the bottom of it to scroll through different troop types. Structures required to research those units are listed at the bottom of the description]
Once you have all required buildings [on required level] you can go to the academy, and you will have the option to 'develop' new unit type. When you are ready, click it, and when its finished, you will be able to build this new unit in one of the army-building structures [barracks, stable, workshop].
Hope that helps.